When you create a play without sharing a formation your players will be lined up at the line of scrimmage with the Center starting the play with the ball:

The center can only snap the ball to players that are behind him in the play so if you look at the “Ball” menu (right-click on a player to trigger their action menu) of any of the other players you’ll see there’s no option to receive the snap:

If you move this player behind the line of scrimmage you’ll see the “Snap” menu is now available under the “Ball” menu:

and clicking “Receive Snap” from this menu will cause the center to snap the ball to this player:

The player who receives the snap now has a “Receive Snap” action in their script:

while the Center has the “Snap Ball” action:

You can remove the snap by removing either of these actions from the appropriate player:

You can also snap the ball by choosing “Snap Ball” from the Center’s “Ball > Snap” menu:

then right-clicking on the player you want the snap to go to (the snap target) and choosing “Receive Snap” from their “Ball” menu:

Snapping to Players in Motion
You’re not limited to snapping to a stationary player – the snap target can be a waypoint too.  Just right click on the waypoint that you want to be the snap target just like you would on a player shape and choose “Receive Snap” from the waypoint’s “Ball > Snap” menu.  The snap will now go to that waypoint: